NATHAN (Spec13): Argues defeasibly in first-order logic.

Nathan (specs1-13) is a relatively fast implementation of a defeasible
reasoner with specificity. It uses arguments of the kind described in
[1,2] and its specificity comparator (LMNOP) is described in [3] which
is a modification of the criterion of Poole.
It solves all basic benchmark problems to the author's satisfaction.
Its limitations in planning applications are due to the limits of its
underlying resolution-refutation linear-input set-of-support
theorem-prover for FOL.
It includes a predicate for unique names. It includes a perl
preprocessor for extracting rules from cases.